This will allow the search suggestion to hook up to multiple search
boxes with `.citizen-search-box` as container. Do note that the default
Citizen suggestion is hardcoded for the primary search, so it only
works for the old core search suggestion module.
This is also a prereq for implementing the Codex search like the one
from Vector.
Mostly based on Vector 2022. Now we target checkbox hacks by the HTML classes
.mw-checkbox-hack-TYPE instead of defining each individually, which would
make it more scalable.